Effect of Habitat Characteristics and Perturbation from Insecticides on the Community Dynamics of Ground Beetles (Coleoptera: Carabidae) on Mixed-Grass Rangeland

Abstract

A study was conducted in 1986 and 1987 to determine the relationships between habitat characteristics and perturbation from insecticides on population and community dynamics of ground beetles collected with pitfall traps at 29 mixed-grass rangeland plots in northwestern South Dakota. Detrended correspondence analysis (DCA) and correlation analysis were used to define ecological gradients underlying changes in community structure of ground beetles. Results indicated that spatial changes in ground beetle communities occurred along gradients of percentage of clay, sand, and silt in soils and coverage of bare ground but were not related to vegetation. Twenty of the plots, located in two 1,400-ha blocks, were treated aerially with malathion liquid spray or carbaryl–bran bait in early July 1986. Pitfall trap catches of the dominant species declined significantly in one or both treatment blocks. However, catches rebounded to or above pretreatment levels a year after treatments. Results from DCA and multiple regression analysis of communities sampled in both years indicated that specific habitat characteristics were associated with immediate changes in community structure after perturbation; communities in habitats with high coverage of Buchloe dactyloides (Nutt.) Engelm., low coverage of Bouteloua gracilis (H.B.K.) Lag. ex Steud., and low clay soils were more resistant to change. Community malleability, or the tendency of communities to return to their predisturbed state, was not affected by treatment and was greater in habitats with high coverage of B. dactyloides and sedges and low coverage of B. gracilis and forbs. These variables are undoubtedly associated with other habitat characteristics as well.